The present invention relates to a process for the recovery of copper contained in solutions from the recovery of iodine from industrial waste streams from the production of ionic and non-ionic iodinated X-ray contrast agents. The process is particularly valuable when the above mentioned waste streams derive from the recovery of iodine by mineralization with finely dispersed metal copper and copper ion solutions.
The recovery of iodine from solutions containing iodinated organic compounds, in particular ionic and non-ionic X-ray contrast agents, is the solution to a both environmental and economic problem.
Iodine has, in fact, to be recovered from the effluents and waste streams from the production of 2,4,6-triiodo-1,3-benzenedicarboxylic acid derivatives due to its high intrinsic cost as well as to the need for reducing the environmental impact deriving from its production.
Law regulations in many Countries have in fact established very strict standards, setting the presence of organic aromatic compounds in waste streams namely to some ppm.
In particular, Italian law does not allow wastes to contain above 0.4 ppm of organic aromatics: it is therefore mandatory for such molecules to undergo degradation while recovering iodine.
This problem has been known for some time, and a number of patent applications concerning the process for the recovery of iodine have been filed (see, for instance: WO 98/07661, WO 94/10083, EP 106934).
More particularly, EP 106,934 discloses a process for the mineralisation of iodine, which comprises heating the recovery solutions containing the ionic and non-ionic contrast agents for a time of 30 minutes-2 hours at a temperature of 100-150xc2x0 C. in the presence of strong alkali and copper ions or finely dispersed copper in amounts ranging from 100 to 2,500 ppm, which can be a further environmental problem.
Patent application WO 00/32303 discloses a process further improving the conditions for the recovery of iodine from industrial wastes from the production of ionic and non-ionic iodinated X-ray contrast agents.
According to the cited patents, iodine can be recovered by use of oxidizing agents such as manganese dioxide, sodium chlorate, hydrogen peroxide, chlorine, sodium hypochlorite, nitrous acid.
Notwithstanding the various patents concerning processes for the mineralisation and recovery of iodine which make use of copper ions or finely dispersed copper, the problem of the recovery of copper from the mineralisation final solutions has yet to be solved.
The toxicity of metals is well-documented in literature and their presence in industrial waste streams may have potentially toxic effect on animal and aquatic life. In fact, while organic pollutants can be subjected to degradation to harmless products, metals do not undergo degradation and can therefore accumulate in the fat tissues of living organisms, reaching concentrations in excess to those which originally existed in air or water.
In order to protect the environment from such contaminants, discharge of heavy metal containing waste streams is subject to strict regulations.
Electronic and pharmaceutical industries, for example, produce high volumes of industrial wastes having a particularly high content in heavy metals and copper ions. These effluents cannot be directly discharged in the environment and have to previously undergo an expensive treatment to ensure the reduction in their metal content.
More particularly, Italian law is very strict as far as the copper residual content dumped in the environment is concerned, setting a maximum tolerance of totally 0.4 ppm of copper in the wastes from a single industrial plant.
The process disclosed in the above cited WO 00/32303 for the recovery of iodine contained in solutions from wastes from the production of ionic and non-ionic contrast agents, makes use of copper ion or finely dispersed copper as a catalyst, in amounts ranging from 100 to 2,500 ppm and this can be an environmental problem.
In literature some processes are known for removing metal ions from aqueous solutions, but not from solutions deriving from the recovery of iodine from waste streams from the production of ionic and non-ionic X-ray contrast agents.
U.S. Pat. No. 5,122,279 discloses a process for removing the copper ion from a solution, which comprises treatment with ferrous dithionate to precipitate the corresponding metal complex from the solution, thus allowing for the metal to be separated.
Furthermore (see for example: U.S. Pat. Nos. 3,640,703, 3,790,370, 5,783,057) some chemical processes for the recovery of copper are known, which involve the use of sodium sulfide or hydrogen sulfide.
However these procedures, while easy to carry out in laboratory, are hardly industrially workable in that the addition of sodium sulfide or hydrogen sulfide causes unavoidable bad smell as well as a high contamination load.
U.S. Pat. No. 4,428,773 discloses a process for the treatment and recovery of copper and copper oxide from industrial wastes, in which copper and copper oxide are precipitated from the solution in alkali medium.
U.S. Pat. No. 4,343,706 discloses a process in which copper is recovered from industrial waste streams by precipitation from the solution at basic pH and in the presence of ferric ions, used both for their reducing properties and for their coagulant and flocculant properties.
Analogously, U.S. Pat. No. 5,472,618 discloses a method for recovering copper, which makes use of the reducing properties of a metal such as iron at acid pH and allows to recover the precipitated metal copper at the end of the treatment.
Some patents concerning the galvanic and metal working industries are known, which disclose (see for example U.S. Pat. Nos. 5,200,473, H0001661, 5,198,021, 4,070,281) the use of chelating cationic resins for removing metal ions from solutions containing the metal complexed for example with cyanide ions.
U.S. Pat. No. 5,262,018 discloses a process for the recovery of metals from solutions deriving from peroxy compounds, which comprises the use of ion exchange resins.
Similarly, the use of ion exchange resins for the recovery of metals is discloses in some process patents (see e.g. U.S. Pat. Nos. 5,907,037, 4,500,396, 5,907,037).
However, the cited literature describes processes for the recovery of both metal and ion copper which are either unsatisfactory or exceedingly costly for such an industrial application.
It has now surprisingly been found, and it is the object of the present invention, a process which, in addition to completely remove copper from the solution, also makes it possible to recover it in the form of a chloride or a sulfate so as to reuse it in the mineralisation process.
The process for the recovery of copper consists of multiple steps which are carried out considering the content in inorganic ions and organic products in the solution deriving from industrial waste streams from the production of ionic and nonionic iodinated X-ray contrast agents.
The present invention relates to a process for the recovery of copper from solutions deriving from the recovery of iodine from production wastes from the production of ionic and non-ionic iodinated X-ray contrast agents.
The process is particularly suitable when the above mentioned waste streams derive from the recovery of iodine by mineralisation with finely dispersed metal copper and copper ions solutions and comprises the following steps:
1. percolating the solution from industrial waste streams on chelating resins suitable for removing copper;
2. displacing copper and regenerating the resins with a 10% hydrochloric acid or 10% sulfuric acid solution.
Step 1 is conducted by percolation on iminoacetic, aminophosphonic or carboxylic resins and it allows to selectively retain copper while discharging the metal-free solution eluted from the column, thus avoiding environmental problems. Suitable resins are selected from the group consisting of: Duolite C467(copyright), Amberlite IRC 86(copyright) and IRC 748(copyright), or commercial equivalents thereof capable of selectively removing copper.
In case of industrial wastes containing high concentrations of chlorides, iodides, sulfates and organic compounds, a preliminary step is preferably carried out to make the recovery of the metal easier and to avoid any precipitations of impurities which could clog the resins.
In this case, the process involves a preliminary treatment of the solution from the effluents from the production of iodinated X-ray contrast agents, which comprises the following steps:
a) filtration through nanofiltration membranes to obtain the iodides in the permeate while retaining copper as a complexed divalent ion in the retentate;
b) oxidation and sublimation of molecular iodine by treating the permeate solution.
Nanofiltration of step a) allows to separate divalent ions from the monovalent ones and the compounds of molecular weight above 150-300 daltons from the smaller ones.
Polyamide membranes having a 98% MgSO4 retention coefficient, for example DESAL5(copyright), FILTEC(copyright) or commercially available analogues, make it possible to separate sodium iodide and sodium chloride from the high molecular organic compounds, phosphates, sulfates and copper as a divalent ion.
By this technique, iodides are fed to the iodine recovery process whereas the residue is treated to remove copper.
As high molecular compounds and di- and trivalent ions remain in the retentate, a solution free from iodides and chlorides is obtained, having a concentration up to 100-5000 ppm of copper. Permeation of iodides and chlorides can be monitored by using a conductimeter.
This operation provides an 80 to 98% copper recovery yield. Iodides are oxidized by addition of an oxidizer selected from the following: manganese dioxide, sodium chlorate, hydrogen peroxide, chlorine, sodium ipochlorite, nitrous acid, preferably sodium chlorate or hydrogen peroxide. The oxidizer concentration can range from 20% to 50% depending on the concentrations of the commercially available solutions. The oxidation can be effected at a temperature ranging from 20xc2x0 C. to 100xc2x0 C., under atmospheric pressure or at most 9 bars. The progress of the process can be monitored by means of the redox potential.
At the end of the oxidation, iodine is separated from copper by sublimation through injection of steam into the mixture. Iodine can be recovered either through a scrubber with water at 17xc2x0 C. or by using 30% (w/w) sodium hydroxide which is subjected to dismutation to iodide and iodate.
The collected solution containing 100-2500 ppm of copper subsequently undergoes treatment for the recovery of the metal as already described at steps 1 and 2.
In some cases, the presence of sulfates, phosphates and organic compounds can cause severe packing problems and precipitation of solid product in resin beds, therefore adversely affecting the efficiency of the elution of the solution.
In order to avoid these problems and to remove tarry substances, a preliminary precipitation of these substances can be carried out by adding the same resin as used to fix copper, subsequently filtering the suspension through paper or sand filter. This operation is unsuited when the resulting solutions contain large amounts of suspended solids and the volumes of solution to treat are high.
This way, the iodine-containing solution is present in the permeate (which is subsequently oxidized) and the copper-containing solution in the retentate.
Alternatively to the precipitation step, the copper-containing solution from industrial waste streams from the production of ionic and non-ionic iodinated contrast agents can be filtered on a pre-column with sand filter, thereby removing the suspended organic compounds before carrying out the process of the invention.
The sand used for this purpose is quartz sand with about 60% 0.2-0.8 mm particle size distribution or sea sand with about 95% 0.1-0.3 mm particle size distribution. The choice depends on the characteristics of the particulate to be removed before the column treatment. The sand filter can be regenerated by back-washing.
This operation is necessary to remove some organic compounds which, if precipitated together with sodium sulfate, clog the resin thus making it useless during the solution percolation and metal recovery step.
The metal is subsequently recovered as a chloride or sulfate, during the resin regeneration step, by using a 5-10% (w/w) hydrochloric acid or sulfuric acid solution.
The solution from the regeneration step can be recycled to the mineralisation process either directly or after concentration. The overall recovery yield of copper is 80-90%. The solutions from this treatment have a copper residual concentration not higher than 1 ppm, preferably not higher than 0.4 ppm.
In this way, considering the other effluents from the treatment of the wastes from the production of contrast agents for the recovery iodine, contaminating effluents with a copper content below 0.4 ppm, which is the maximum value admitted by Italian law, can be fed, for example, to a plant for the biological treatment of contaminants.
The process of the invention is reported in greater detail in the experimental section.